Human Anatomy
Nervous Tissue Histology
Nervous tissue histology for MBBS: neuron types, Nissl bodies, glial cells, myelination and peripheral nerve coverings, mapped to NMC codes AN68.1 to AN68.3.
MedNext Academy | 3 min read
Nervous Tissue Histology
Nervous tissue histology for MBBS: neuron types, Nissl bodies, glial cells, myelination and peripheral nerve coverings, mapped to NMC codes AN68.1 to AN68.3.
This chapter describes the structure of neurons and the supporting glial cells and identifies them under the microscope. It correlates neuronal structure with function and covers the arrangement of peripheral nerves and ganglia.
High-yield: Nervous Tissue Histology
- Nervous tissue is made of neurons that conduct impulses and neuroglia that support them.
- A typical neuron has a cell body, dendrites that receive impulses and a single axon that conducts them away.
- Multipolar neurons have many dendrites and one axon and are the commonest type, as in motor neurons.
- Unipolar or pseudounipolar neurons are found in the dorsal root ganglia and carry sensory information.
- Bipolar neurons have one dendrite and one axon and occur in the retina and olfactory epithelium.
- Nissl bodies are stacks of rough endoplasmic reticulum in the cell body and dendrites, absent from the axon hillock.
- The central glia are astrocytes, oligodendrocytes, microglia and ependymal cells.
- Oligodendrocytes myelinate axons in the central nervous system, each wrapping several axons.
- Schwann cells myelinate axons in the peripheral nervous system, each forming one internode of one axon.
- Astrocytes support neurons, form the blood-brain barrier with capillaries and repair by gliosis.
- Microglia are the resident phagocytes of the central nervous system, derived from monocytes.
- The nodes of Ranvier are gaps in the myelin that allow saltatory conduction of the impulse.
- A peripheral nerve is wrapped by endoneurium around each fibre, perineurium around fascicles and epineurium around the whole nerve.
- Sensory ganglia contain pseudounipolar cell bodies surrounded by satellite cells.
- After injury the peripheral axon can regenerate because the Schwann cells and endoneurial tube guide regrowth.
Neurons and supporting cells
- **Multipolar neuron:** Many dendrites, one axon. Commonest type, as in motor neurons.
- **Pseudounipolar neuron:** Single process that divides; sensory, found in dorsal root ganglia.
- **Myelinating glia:** Oligodendrocytes in the central nervous system; Schwann cells in the peripheral nervous system.
- **Nerve coverings:** Endoneurium around fibres, perineurium around fascicles, epineurium around the whole nerve.
NMC competencies in this chapter
- **AN68.1:** Identification of multipolar and unipolar neurons, ganglia and peripheral nerve
- **AN68.2:** Structure-function correlation of the neuron
- **AN68.3:** Ultrastructure of nervous tissue
Frequently Asked Questions
What are the main types of neuron by shape?
Multipolar neurons with many dendrites and one axon, bipolar neurons with one dendrite and one axon, and pseudounipolar neurons with a single dividing process, found in sensory ganglia.
What is the difference between oligodendrocytes and Schwann cells?
Oligodendrocytes myelinate central axons and can each myelinate several axons, while a Schwann cell myelinates a single internode of one peripheral axon.
What are Nissl bodies?
They are clumps of rough endoplasmic reticulum in the neuronal cell body and dendrites that stain deeply. They are absent from the axon hillock and the axon.
Why can peripheral nerves regenerate but central axons cannot?
Schwann cells and the endoneurial tube guide and support regrowth in the peripheral nervous system. In the central nervous system the glial environment and scar formation inhibit regeneration.
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